The present invention relates generally to circuits and methods for external configuring of the identification address of a sensor-to-digital-bus interface device without providing dedicated identification address configuration pins on a package containing the interface device.
Communication busses, such as I2C buses, frequently require unique addressing information for each device (such as a sensor interface device) connected to the bus. A device often requires address configurability to ensure that the device is unique in a large number of possible system implementations and/or to allow multiple identical devices to be installed on the same bus in the same system. Providing one or more dedicated address configuration package pins to be connected by conductive “straps” to ground or to the VDD supply voltage is a common way of accomplishing this.
The closest prior art is believed to be the use of the above mentioned conductive “straps” to configure the identification address of a device, such as a sensor interface device which couples a sensor to a digital bus. The way I2C systems operate is that an I2C device which presently is the “master” in charge of the I2C bus can send an address on the bus, and that address will be recognized by an I2C slave device which has a pre-configured “identification address” which matches the “requested address” on the I2C bus. The matching slave device then sends an acknowledge signal on the serial data bus, after which the master device can communicate with that slave device via the I2C bus.
Referring to FIG. 1, I2C system 1 includes an I2C master device 2 having a SCL (serial clock) terminal connected to a SCL bus conductor 3 and a SDA (serial data) terminal connected to a SDA conductor 4. System 1 also includes four sensor interface devices 5-1, 5-2, 5-3 and 5-4 each having a SCL terminal connected to SCL bus conductor 3 and a SDA terminal connected to SDA bus conductor 4. (Any of the sensor interface devices 5-1, 5-2, 5-3 and 5-4 may also be referred to herein simply as “sensor interface device 5”.) Each sensor interface device 5 includes 2 terminals DXP1 and DXN1 which can be connected to one external sensor, and also includes 2 more terminals DXP2 and DXN2 which can be connected to another external sensor. Each external sensor in Prior Art FIG. 1 is illustrated as a diode-connected PNP transistor which is utilized to sense ambient temperature (although the external sensor also could be an NPN transistor or other sensor). In sensor interface device 5-1, DXP1 and DXN1 are connected to the emitter and collector-base of temperature-sensing PNP transistor Q0, and similarly, DXP2 and DXN2 are connected to the emitter and collector-base of temperature-sensing PNP transistor Q1. (The collector electrode and base electrode of a diode-connected transistor are collectively referred to herein as the “collector-base,” of the transistor.) Temperature-sensing PNP transistors Q2 and Q3 are similarly connected to sensor interface device 5-2, and so forth. The terminals DXP1, DXN1, DXP2 and DXN2 in FIG. 1 are used only for temperature sensing, and play no role in configuration of the device identification addresses.
Each sensor interface device 5 in FIG. 1 also includes two identification address configuration pins A0 and A1. Identification address pins A0 and A1 of sensor interface device 5-1 are connected to ground to configure its identification address as “00”. Similarly, identification address pins A0 and A1 of sensor interface device 5-2 are connected to VDD and ground, respectively, to configure its identification address as “01”. Address pins A0 and A1 of sensor interface device 5-3 are connected or “strapped” to ground and VDD, respectively, to configure its identification address as “10”, and address pins A0 and A1 of sensor interface device 5-4 are connected to VDD to configure its identification address as “11”. Transistors Q0, Q2, Q4 and Q6 all are connected in exactly the same way to the DXP1 and DXN1 terminals of the various sensor interface devices, and transistors Q1, Q3, Q5 and Q7 all are connected in exactly the same way to the DXP2 and DXN2 terminals of the various sensor interface devices.
The two address configuration pins A0 and A1 of each sensor or face device 5 are internally coupled, either directly or by means of latches, to comparator circuitry which compares the pre-configured device identification address to a requested address provided by master device 2 via the SDA bus. A0 sets the LSB (least significant bit) of the sensor interface device address and A1 sets the next-least-significant bit thereof. Connection of either the A0 pin or the A1 pin to ground represents a “0”, and connection of either the A0 pin or the A1 pin to VDD represents a “1”.
However, the substantial cost of providing the above described dedicated address configuration pins on the packages of the sensor interface devices is a significant drawback of the prior art techniques.
Thus, there is an unmet need for reducing the cost of configuring the device identification address of sensor interface device for coupling an external sensor to a digital bus.
There also is an unmet need for a circuit and method for configuring a device identification address of a sensor interface device without requiring a dedicated device identification address configuration pin on a package containing the sensor interface device.
There also is an unmet need for a circuit and method for reducing the cost and size of a sensor interface device by reducing the its required number of package pins.